tcg bug master / 4.0.0 v8 operation >>> and |=

[manuel baesler]

vm guest is linux, executed with tcg
running this Node.js snippet leads to

$ node
> a = undefined
undefined
> a >>> 0
4294967295

host node
$ node
> a = undefined
undefined
> a >>> 0
0

same with |=

node
Welcome to Node.js v12.4.0.
Type ".help" for more information.
> let buffer
undefined
> buffer |= 0
0

vm with tcg:

$ ./out/Release/node --version
v12.4.0
./out/Release/node -e "let buffer; buffer |= 0; console.log(buffer);"
-1

vm guest is debian x86_64 latest release
vm guest is started with ./x86_64-softmmu/qemu-system-x86_64 -vnc :0 -cdrom debian-9.9.0-amd64-netinst.iso -m 4G -smp cores=6,threads=1,sockets=1 -nic user,hostfwd=tcp:ipv4addr:2233-:22 -cpu qemu64 debian.img

git tag v4.0.0 and master, commit a578cdfbdd8f9beff5ced52b7826ddb1669abbbf, for building qemu-system-x86_64 was used.

Node.js is compiled on the vm guest (v12.4.0 / master)

see also
https://github.com/nodejs/node/issues/19348#issuecomment-500465502

I need further assistance to track down the cause of the bug.

Kind regards
Manuel

[Peter Maydell (pmaydell)]

This might be the same underlying problem as LP:1815423 which also mentions some issues with Javascript calculations involving arithmetic operations on a js "undefined" value. That bug has a C-only reproduce case so is probably a good place to start for anybody interesting in investigating and fixing it.

[Peter Maydell (pmaydell)]

https://<email address hidden>/ is a patch which I think probably fixes this bug -- could you test it? (I don't have an x86 vm with node.js in it to test with.)

[manuel baesler (manuelbaesler)]

Hi Peter,

I will try the tag and report back.

[manuel baesler (manuelbaesler)]

result:

node
Welcome to Node.js v12.4.0.
Type ".help" for more information.
> a = undefined
undefined
> a >>> 0
0
> let buffer
undefined
> buffer |= 0
0

Thanks for the patch :-)

[Peter Maydell (pmaydell)]

Thanks a lot for testing it!

[Thomas Huth (th-huth)]

Patch had been included here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=1e8a98b53867f61da9c